An optical attenuator is a device which is widely used in a variety of modern telecommunications applications. It provides balance of optical power levels of data transmission, including balancing of signal-to-noise ratio and power levelling between different wavelengths in a wavelength division multiplexing (WDM) system. Usually there is a large number of attenuators distributed throughout the system, the particular patterns dictated by the geometry of the network (long haul, ring, metro, etc.). Because of an increasing use of these elements, small, efficient and easily controllable attenuators become an important requirement.
There is a variety of types of optical attenuators developed up to date. As an example, they include waveguides with electronically variable properties, macroscopic mechanical means of attenuating light, and micro-mechanical structures brought by the rapid advances of the micro-electro-mechanical system (MEMs) technology during the past ten years. Material thicknesses and feature sizes of 1 micron and sub-micron dimensions are typical as a result of the use of high definition photolithography techniques, but having the ability to fabricate these structures is only the first step. The next is to provide an efficient use of such devices by an easy and controllable attenuation of light up to sub-dB range of accuracy.